That is a bit of a load question because light and the direction it come from can change what your eye process and effect your groups.
I am no expert at all, but when I took a Defoor pistol class he said that "your eye are drawn to movement, color, and then shape." His sights which I shoot are all black and have a 5 inch width at 25 yards. He shoots all of 25 yard bull eyes in his class and likes for you to be able to perform a score of 90 or better on them. He uses black because light has the least amount of affect on that color. He also released a new sight that he was still in testing when I took his class that has tritium in the lower part of the front. This all you to keep your precision at distance, but during low light shooting if you can see the dot your not on target.
I would recommend the video link below by Mike Pannone which is one of the best in the business. He brings up all points about sight and you can use that information to help guide your decision.
